1. Field of the Invention
The invention relates to a needle for use in cataract extraction surgery of a persons eye.
2. Description of the Prior Art
In modern cataract extraction surgery, particularly phacoemulsification, one feature of the surgical technique is to separate and loosen the central nucleus from the surrounding cortex material. By loosening the nucleus, it increases accessibility for phacoemulsification by the phacoemulsifier. A common technique used for separating the central nucleus from the peripheral cortex is by means of hydrodissection, in which fluid, generally physicologic saline (balance salt) is forcibly injected through a needle which has been inserted into the lens material. When the needle tip has reached the proper anatomic level, within the lens, the fluid which has been injected through the needle under force from a syringe will seek, dissect and develop a natural cleavage plane between the hard central nucleus and the softer peripheral cortex. As fluid is further injected through the needle tip, the hydrodissection continues until the separation is complete. Critical to the success of this technique is the ability to place the needle tip in the proper anatomic location within the lens material. This depends on both the skill of the surgeon, and the ability of the needle to penetrate the lens material. It further relates to the adequate and proper functioning of the needle during fluid injection.
In general, there are 2 approaches for hydrodissection of the lens nucleus. One is an automated technique using a technology called Hydrosonics, in which a thin, hollow, mechanically driven, rapidly vibrating needle is introduced into the lens material. By virtue of the needle vibration, and injections of small increments of fluid through the needle, the needle penetrates into and separates the central nucleus from the peripheral epinucleus or cortex. This technique has the advantage of being capable of a very detailed and precise delineation of the central nucleus from the peripheral lens material. Additionally, because of its great penetrating capabilities, the vibrating needle can in fact, soften an otherwise hard central nucleus making it easier for phacoemulsification to be performed subsequently. Because it is automated, it is a technique that is somewhat easier to accomplish than using the manual techniques described below.
However, in view of the very adequate phacoemulsification machines available, the ability of the Hydrosonics technology to soften the central nucleus in addition to separating it from the peripheral cortex is possibly unnecessary, superfluous and somewhat "overkill" and represents capabilities which are beyond the usual need of the hydrodissection needle per se. Finally, the Hydrosonics technology has the disadvantage of being considerably more expensive than the manual techniques.
Manual techniques used for nucleus loosening and separation also involve a needle which is introduced into the lens material of the eye and through which fluid is injected, the fluid then separating the central nucleus from the peripheral cortex. The manual techniques, however, differ from the automated technique in that the needle is not vibrating or mechanically driven by automated technology in any way. The needle is simply introduced by hand by the surgeon passing the needle through the cataract incision and into the lens substance.
Various needles have been designed with different tip configurations to accomplish manual hydrodissection. One general basic design is that of a tapered blunt-tipped needle with a central opening at the end of the tip through which the fluid is injected. This design has the considerable disadvantage of introducing the irrigation port first as the leading part of the hydrodissection needle, directly into the lens material which allows for easy plugging of the irrigation port by the lens material as the needle progresses into the lens substance. Plugging of the irrigation port of the hydrodissection needle is a considerable disadvantage to the design which in fact may render the hydrodissection needle essentially non-functional due to the inability to irrigate fluid through the irrigation port. The needle may either be totally non-functional due to complete plugging by lens material in the irrigation port, or partially non-functional, the blockage being finally freed from the irrigation port when elevated irrigation pressure is applied, a situation which can be hazardous when performed with the needle tip inside the eye during surgery.
Another flaw in this particular design is that the tip itself is otherwise blunt and not as easily passed into the lens material as a sharp-tipped needle would be. A final flaw in this design is that fluid irrigation into the lens material occurs only at one anatomic level, that being the level of the single irrigation port at any given time. This limitation of irrigation to the anatomic location of a single irrigation port requires considerably greater precision in proper placement of that irrigation port within the lens material making the procedure much more difficult requiring an undesirable degree of accuracy in placement of the needle tip.
Other needles have been designed in the past which, while not being designed specifically for hydrodissection would alleviate some but not all of the afore mentioned design flaws of: 1) end on location of the irrigation port; 2) limitation to a single irrigation port; 3) blunt-tipped needle.
One hydrodissection needle, converts the generally round configuration of the afore mentioned hydrodissection needle to a flat configuration which would allow easier passage through the lens substance. This design, however, continues to have the problems with end on irrigation which is limited to a single port with a blunt tip. An additional design, the Bishop-Harmon anterior chamber needle, converts the end on irrigation port to an oval configuration which conceivably would give a slightly broader irrigation range to the sides. Another needle possesses a sharp tip, but still with an end opening.
Needles with multiple irrigating ports have also been utilized, with the location of the irrigating ports occupying simultaneously the end of the needle, and the side needle shaft. This particular design, however, has the difficulty of having a blunt end.
Attempts to solve the difficulties of blunt-end have been addressed in the Shahinian lacrimal cannula, this cannula actually being used for irrigation of the nasal lacrimal tear duct system and not for hydrodissection. It does have the features of a modestly pointed tip with the irrigating port located behind the tip. An additional needle which is actually used for suturing, is the Simco suturing needle which has a sharp point, and end-on irrigation port and a second port which conceivably could be used for irrigation located somewhat behind the tip.
Many other needles have also been designed with an irrigation port located proximal to the distal cannula or needle tip. These various alterations, have not been sharp or in any way configured to allow introduction into the lens material.
Finally, additional "needle" or cannula designs have incorporated double cannulas with an irrigating port located on one needle which is immediately adjacent to a second needle which has an additional irrigation port. Again, these needles are not designed for hydrodissection in that they do not have a sharp tip and the double cannula configuration is extremely bulky and unusable for hydrodissection.
Thus the prior art afore mentioned needles and cannulas, have design flaws namely being: 1) end-on location of the port; 2) presence of a single irrigating port; 3) blunt tip; 4) irrigation port configuration limited to a round or flattened hole at or near the end of the hydrodissection needle.